Sell the sub on craigslist and put a title like "BANGIN TRUCK SUB $1"
and a body like this:
"Yeah brah dis sub bangs relly hawd foda money. It may be little but its a banga. Lookin for 75 OBO".
You will surely get some idiot who will offer you 50. sell it to him and start off there. When selling on CL sound like an idiot. thats the key. I can recommend a 1000 50 dollar subs that would be better than that. Not trying to bash you man just trying to help you get it halfway right the first time, and besides, there is no better feeling than spending a couple hours hooking up a system to find out it blows. To fund a decent amp to pair it up, you could just sell some xbox games or whatever youre into. I promise it would be better to save up and have a 150-200 dollar sub/amp budget than roll with what you got. Nobody likes starting out on this website because of this lol. But again there is nothing better than a disappointing setup and or the smell of burnt subs.
EDIT: For the money you have. there are tons of people selling used amps and small subs for cheap here. 55bucks for a used E8 from sundown that would blow that Dual box to pieces.